$\begingroup$which broker did you use? what about the P&L once you close out the futures contract - was it automatically converted back to USD?$\endgroup$
– udayDec 24 '15 at 17:28

$\begingroup$I cannot disclose the broker that I use since I work for a firm, but yes automatically converted to USD using their fx princing for the day you close the position$\endgroup$
– FernandoGDec 24 '15 at 17:35

$\begingroup$@pyCthon, thanks for the link. it was very useful$\endgroup$
– udayDec 25 '15 at 6:13

$\begingroup$In my experience with various brokers (including IB) this is not what happens at all. Once your trading creates a balance in JPY (positive or negative) you account becomes a multi-currency account, with separete balances in USD and JPY. There is no automatic conversion of JPY to USD and it is entirely up to you to make such conversion if and when you want. Of course, if your base currency is USD, the broker, as a courtesy, shows you the overall value of your account translated to USD at current fx rates, but you still have (pos or neg) balances in each of the two currencies.$\endgroup$
– noob2Dec 28 '15 at 14:51